1. Field of the Invention
The present invention relates to a communication system, and more particularly, to a receiving apparatus in a communication system and related method.
2. Description of the Prior Art
A conventional DC offset calibration scheme applied in a receiving system usually adopts an AC coupling to filter out the DC offset in a signal or performs a current compensation to calibrate the DC offset in the signal. However, since a conventional AC coupling need enough response time (also called frequency response time) to correctly operate, the total response time of the receiving system will become much longer if an AC coupling is applied in each amplifying circuit or each filtering circuit to filter out DC offset of the signal in the signal.
On the other hand, if a current compensation operation is used for calibrating the DC offset in the signal, it is not only required to wait for a predetermined period to determine a current amount for compensation, but also consumes more power than the AC coupling since it utilizes the current amount for compensation. Furthermore, a determined compensation current is easily affected by changes in operating temperature and/or operating voltage. Practically, it is very difficult to predict any randomized DC offset caused by self-mixing in a mixer, local oscillator (LO) leakage, or other noise in front-circuit of the receiving system. Thus, the current compensation operation cannot accurately calibrate the DC offset in the above-described signal. That is, even though the current compensation circuit can calibrate the DC offset caused by transistor mismatch from amplifying circuits or filtering circuits in the receiving system, it cannot accurately calibrate the DC offset caused by the self-mixing in the mixer, the LO leakage, or other noise.